This invention relates to catalysts useful in polymerizing xcex1-olefins. In particular, it relates to the polymerization of ethylene using transition metal catalysts with bidentate ligands containing pyridine or quinoline moieties.
Until recently, polyolefins have been made primarily using conventional Ziegler catalyst systems. A Ziegler catalyst typically consists of a transition metal-containing compound and one or more organometallic compounds. For example, polyethylene has been made using Ziegler catalysts such as titanium trichloride and diethylaluminum chloride, or a mixture of titanium tetrachloride, vanadium oxytrichloride, and triethylaluminum. These catalysts are inexpensive but they have low activity and therefore must be used at high concentrations. The catalyst residue in the polymers produce a yellow or grey color and poor ultraviolet and long term stability, and chloride-containing residues can cause corrosion in polymer processing equipment. It is therefore sometimes necessary to either remove catalyst residues from the polymer or add neutralizing agents and stabilizers to the polymer to overcome the deleterious effects of the residues and this adds to production costs. Furthermore, Ziegler catalysts produce polymers having a broad molecular weight distribution, which is undesirable for some applications such as injection molding. They are also poor at incorporating xcex1-olefin co-monomers, making it difficult to control polymer density. Large quantities of excess co-monomer may be required to achieve a certain density and many higher xcex1-olefins, such as 1-octene, can be incorporated at only very low levels, if at all.
Although substantial improvements in Ziegler catalyst systems have occurred since their discovery, these catalysts are now being replaced with recently discovered metallocene catalyst systems. A metallocene catalyst typically consists of a transition metal compound that has one or more cyclopentadienyl ring ligands. Metallocenes have low activities when used with organometallic compounds, such as aluminum alkyls, which are used with traditional Ziegler catalysts, but very high activities when used with aluminoxanes as cocatalysts. The activities are generally so high that catalyst residues need not be removed from the polymer. Furthermore, they produce polymers with high molecular weights and narrow molecular weight distributions. They also incorporate xcex1-olefin co-monomers well.
However, at higher temperatures metallocene catalysts tend to produce lower molecular weight polymers. Thus, they are useful for gas phase and slurry polymerizations of ethylene, which are conducted at about 80xc2x0 C. to about 95xc2x0 C., but in general they do not work well as temperatures are increased. The polymerization of ethylene in solution is desirable because it allows great flexibility for producing polymers over a wide range of molecular weights and densities as well as the use of a large variety of different co-monomers. Solution polymerization permits the production of polymers that are useful in many different applications. For example, both high molecular weight, high density polyethylene (PE) film useful as a barrier film for food packaging and low density ethylene co-polymers with good toughness and high impact strength can be made.
We have discovered novel bidentate pyridine transition metal compounds which have excellent activity as xcex1-olefin polymerization catalysts. We have also discovered that bidentate quinoline transition metal compounds, which were heretofore unsuspected of possessing any catalytic properties, are also excellent polymerization catalysts for xcex1-olefins. These catalysts produce polymers having properties very close to the properties of polymers produced using metallocene catalysts. That is, the polymers have a narrow molecular weight distribution and a uniform co-monomer incorporation.
The transition metal catalysts of this invention containing the bidentate pyridine based ligand have the general formula 
where Y is O, S, NR, PR, 
each R is independently selected from hydrogen, C1 to C6 alkyl, or C6 to C14 aryl, each Rxe2x80x2 is independently selected from R, C1 to C6 alkoxy, C7 to C20 alkaryl, C7 to C20 aralkyl, halogen, or CF3, M is a Group 3 to 10 metal, each X is independently selected from halogen, C1 to C6 alkyl, C6 to C14 aryl, C7 to C20 alkaryl, C7 to C20 aralkyl, C1 to C6 alkoxy, or 
xe2x80x83L is X, cyclopentadienyl, C1 to C6 alkyl substituted cyclopentadienyl, indenyl, fluorenyl, or 
xe2x80x9cnxe2x80x9d is 1 to 4;
xe2x80x9caxe2x80x9d is 1 to 3;
xe2x80x9cbxe2x80x9d is 0 to 2;
a+bxe2x89xa63;
xe2x80x9ccxe2x80x9d is 1 to 6; and
a+b+c equals the oxidation state of M.
In the formula, the Y group is preferably oxygen as those compounds are easier to make. For the same reason the R group is preferably methyl and all of the Rxe2x80x2 are hydrogen. The L group is preferably halogen, most preferably chlorine, as those catalysts give superior properties and are easier to prepare. For the same reasons, the X group is preferably halogen, especially chlorine. The M group is preferably a Group 3 to 7 metal, most preferably a Group 4, 5 or 6 metal such as zirconium, hafnium or titanium.
In a preferred embodiment of the invention
a+bxe2x89xa62 when the oxidation state of M is 4 or less; and
a+bxe2x89xa63 when the oxidation state of M is greater than 4.
With the latter, a+b most preferably is less than or equal to 2 when the oxidation state of M is greater than 4.
Preparation of the bidentate pyridine complexes is illustrated in the examples, but generally they can be prepared by reacting a substituted pyridine precursor having an acidic proton with a compound having the formula MX3L in the presence of an HX scavenger. The reaction is stoichiometric and stoichiometric amounts of scavenger are preferred. Examples of suitable scavengers include compounds that are more basic than the substituted pyridine, such as triethylamine, pyridine, sodium hydride, and butyl lithium. If the scavenger is a stronger base than the substituted pyridine one can make a salt of the substituted pyridine and begin with that. While the reaction is preferably performed in a solvent, only partial solubility of the reactants is required. An aprotic solvent, such as tetrahydrofuran (THF), ether, toluene, or xylene, can be used at about 0.2 to about 20 wt% solids, and preferably at about 5 to about 10 wt% solids. The reaction can occur at about xe2x88x9278xc2x0 C. to about room temperature. As the reaction proceeds a precipitate is formed and the product can be extracted with toluene, methylene chloride, diethyl ether, or a similar extractant.
The bidentate quinoline transition metal catalysts of this invention have the general formula 
where R, Rxe2x80x2, L, M, X, xe2x80x9cnxe2x80x9d, xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d were as previously defined.
The quinoline transition metal catalysts are made in a similar manner to the pyridine transition metal catalysts except that one begins with a substituted quinoline such as 8-hydroxy quinoline (also known as 8-quinolinol) instead of the substituted pyridine. Also, butyl lithium can be used in a solvent to make the lithium salt of 8-hydroxy quinoline, which can also be used as the starting material.
The catalysts of the invention are normally used in combination with a co-catalyst. Such cocatalysts (or activators) are any compound or component which can activate the catalyst. Representative co-catalysts include alumoxanes and aluminum alkyls of the formula Al(R7)3 wherein R7 independently denotes a C1-C6 alkyl group, hydrogen or halogen. Exemplary of the latter of such co-catalysts are triethylaluminum, trimethylaluminum and tri-isobutyl aluminum. The alumoxanes may be represented by the cyclic formulae (R15xe2x80x94Alxe2x80x94O)g and the linear formula R15(R15xe2x80x94Alxe2x80x94O)s AlR15 wherein R15 is a C1-C5 alkyl group such as methyl, ethyl, propyl butyl and pentyl, g is an integer from 1 to about 20 and s is about 2 to about 10. Preferably, R15 is methyl and g is about 4. Representative but non-exhaustive examples of alumoxane co-catalysts are (poly)methylalumoxane (MAO), ethylalumoxane and diisobutylalumoxane.
The mole ratio of such co-catalysts to catalyst when used in a polymerization is generally in the range 0.01:1 to 100,000:1, and preferably ranges from 1:1 to 10,000:1.
An alternative co-catalyst is an acid salt that contains a non-coordinating inert anion (see U.S. Pat. No. 5,064,802). The acid salt is generally a non-nucleophilic compound that consists of bulky ligands attached to a boron or aluminum atom, such as lithium tetrakis(pentafluorophenyl) borate, lithium tetrakis(pentafluorophenyl)aluminate, anilinium tetrakis(pentafluorophenyl)borate, and mixtures thereof. The anion which results when these compounds react with the catalyst is believed to be weakly coordinated to the metal-containing cation. The mole ratio of acid salt to catalyst can range from about 0.01:1 to about 1000:1, but is preferably about 1:1 to 10:1. While there is no limitation on the method of preparing an active catalyst system from the catalyst and the acid salt, preferably they are mixed in an inert solvent at temperatures in the range of about xe2x88x9278xc2x0 C. to about 150xc2x0 C. They can also be mixed in the presence of monomer if desired. The acid salt can be used in combination with the above referenced cocatalysts described earlier.
The catalyst and co-catalyst can be used on a support such as silica gel, alumina, silica, magnesia, or titania, but supports are not preferred as they may leave contaminants in the polymer. However, a support may be required depending upon the process being utilized. For example, a support is generally needed in gas phase polymerization processes and slurry polymerization processes in order to control the particle size of the polymer being produced and in order to prevent fouling of the reactor walls. To use a support, the catalyst and co-catalyst are dissolved in the solvent and are precipitated onto the support material by, for example, evaporating the solvent. The co-catalyst can also be deposited on the support or it can be introduced into the reactor separately from the supported catalyst.
The catalyst is used in a conventional manner in the polymerization of olefinic hydrocarbon monomers. While unsaturated monomers such as styrene can be polymerized using the catalysts of this invention, it is particularly useful for polymerizing xcex1-olefins such as propylene, 1-butene, 1-hexene, 1-octene, and especially ethylene.
The catalyst is also useful in a conventional manner for copolymerizing mixtures of unsaturated monomers such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, and the like; mixtures of ethylene and di-olefins such as 1,3-butadiene, 1,4-hexadiene, 1,5-hexadiene, and the like; and mixtures of ethylene and unsaturated comonomers such as norbornene, ethylidene norbornene, vinyl norbornene, norbornadiene, and the like.
The catalysts of this invention can be utilized in a variety of different polymerization processes. They can be utilized in a liquid phase polymerization process (slurry, solution, suspension, bulk phase, or a combination of these), in a high pressure fluid phase, or in a gas phase polymerization process. The processes can be used in series or as individual single processes. The pressure in the polymerization reaction zones can range from about 15 psia to about 50,000 psia and the temperature can range from about xe2x88x9278xc2x0 C. to about 300xc2x0 C.